Explain mechanistically why it is possible to alkylate a phenol selectively in the presence of a

step 1 Explain the reason for the following observations. Phenol does not react readily with PCL5 to fo

Explain mechanistically why it is possible to alkylate a...

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Key Concepts

Nucleophilic Substitution (SN2) Mechanism

The phenolate ion, being a strong nucleophile, can efficiently attack an alkyl electrophile via an SN2 mechanism. The reaction proceeds with backside attack, leading to the substitution of the leaving group with the alkyl chain, effectively alkylating the phenol. Meanwhile, the less nucleophilic alcohol, which remains in its neutral form, does not participate significantly in the reaction.

Acidity and pKa Difference

Phenols are significantly more acidic than alcohols due to the resonance stabilization of the phenolate ion that forms upon deprotonation. This difference in pKa ensures that under basic conditions, the phenol is selectively deprotonated to generate a highly reactive nucleophilic phenolate, while the less acidic alcohol remains largely protonated and less reactive.

Selective Deprotonation

When a base is added, the phenol undergoes deprotonation preferentially because of its lower pKa, which leads to the formation of a phenolate ion. This selective deprotonation strategy allows the chemist to target the phenol for further reaction (alkylation) without affecting the alcohol functional group.

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